A Fast Background Frequency Calibration Based on Intermittent Frequency Locked Loop for the Super-Regenerative Receive

Abstract

The conventional phase-locked loops or frequency-locked loops should take time to calibrate the oscillator’s resonant frequency in a super-regenerative receiver (SRR) and severely disrupts the receiver’s operations. This paper proposes a novel intermittent frequency locked loop (IFLL) as a frequency synthesizer to continuously maintain the resonant frequency equal to the preset target frequency without interruption to the SRR. An analog loop mainly composed of a time-register-based frequency detector and a charge pump is proposed to achieve precise frequency detection during each SRR’s quenching period regardless of the inevitable initial phase error, and adjust SRR’s resonant frequency accordingly. An average fractional division scheme is adopted to improve IFLL’s frequency resolution to the level of the quenching frequency. The operations of the IFLL are analyzed with the z-domain transfer function, including the stability and frequency response. A prototype is built and tested. The measurement results show that the proposed IFLL only needs a calibration cycle of fewer than 50 $\mu \text{s}$ to adjust SRR’s resonant frequency without interruption against its receiving. The real-time frequency error after calibration is smaller than 70 kHz. SRR opposes a sensitivity of −61.2 dBm @ 200 kbps and a 3-dB bandwidth of 2.2 MHz.

Keywords

• Average fractional division scheme
• background frequency calibration
• frequency-locked loop
• initial phase error
• phase-locked loop
• super-regenerative receiver